1. Field of the Invention
The present general inventive concept relates to an image forming apparatus, and more particularly, to a fusing device to fix a developer image onto a recording medium, and an image forming apparatus having the same.
2. Description of the Related Art
Generally, an image forming apparatus such as a printer, a copier, a scanner, a multi-function unit (MFU), or a facsimile, employs a fusing device to fix a developer image onto a recording medium after the developer image is transferred onto the recording medium by a transfer device. The fusing device is mainly classified into roller type and belt type devices.
In compliance with demands for a faster image forming apparatus, a fusing device, which is capable of heating and fusing at a high speed, is required. For faster heating, it is necessary that the heating part have a lower heat capacity. Also for a better fusing performance, a wider nip area and a more effective pressing on a developer image are required so that heat from the heating part can be transmitted to the image more effectively.
However, the currently available roller or belt type fusing device are obstacles to the development of a high speed image forming apparatus, because it does not meet the requirements for fast heating and good fusing performance. The general example of roller and belt type fusing devices will be explained briefly below.
FIG. 1 illustrates a general roller type fusing device. As illustrated, a roller type fusing device includes a pressing roller 10, a heating roller 20 rotated in tight contact with the pressing roller 10, and a heating part 30 disposed inside the heating roller 20.
The roller type fusing device fixes a developer image (T) onto a recording medium (P) by heating and pressing, when the recording medium (P) passes a nip area (N) generated on the pressing roller 10 and the heating roller 20 by a squeezing of the pressing roller 10 and the heating roller 20 against each other. The roller type fusing device has less of a temperature drop, so high speed printing is possible. However, because the heating roller 20 has a high heat capacity and the heating part 30 has to heat the entire heating roller 20, warm-up takes a considerable time. Furthermore, because nip areas (N) are formed as the two rollers 10 and 20 are squeezed against each other, sufficiently wide nip areas (N) cannot be provided. It is also difficult to variably shape the nip areas (N) according to need.
FIG. 2 illustrates a general conventional belt type fusing device. As illustrated, the belt type fusing device includes a pressing roller 10, a fusing belt 40 to rotate with a supply of rotational force being transmitted from the pressing roller 10, a guide member 50 disposed inside the fusing belt 40 to guide the rotation of the fusing belt, and a heating part 60 disposed on the guide member 50 to heat the nip area (N) on the fusing belt 40.
The heating part 60 of the belt type fusing device has a low heat capacity. Because local heating focused on the nip area (N) is possible in the belt type fusing device, a shorter time is required for warm-up than by the roller type fusing device of FIG. 1, and a wider nip area (N) is provided. However, because the heating part 60 is provided at the nip area (N) and pressed by the pressing roller 10, the pressing force of the pressing roller 10 is limited. Accordingly, pressure is not exerted to the nip area (N) effectively, deteriorating the fusing quality. If the pressure at the nip area (N) is increased to improve fusing quality, the heating part 60 may be damaged due to pressure and heat deformation.